PROJECT SUMMARY/ABSTRACT Migraine affects 12% of the world population, and is one of the leading causes of disability worldide. Yet surprisingly little is known about the basic features of this disease. One of the major questions in migraine is how its quintessential feature, the migraine attack, is generated. For approximately a third of migraineurs, the pain of the attack is preceded by an aura, typically a sensory hallucination. Unlike the attack, the aura is physiologially measurable, in humans and in animal model systems, because its physiological correlate is a massive depolarization called cortical spreading depression (CSD). By understanding how CSD is generated, we can understand how the attack begins. Our three aims address the origins of the migraine attack from different angles. The first aim builds on our work showing that CSD, like the aura, has a predilection for sensory cortex. We ask why this predilection exists, with the expectation that understanding the mechanisms will yield insights as to how the aura, and thus the attack, are generated. We use a combination of imaging, electrophysiology and transporter expression analysis to examine the reuptake of extracellular potassium and glutamate, with the hypothesis that barrel cortex may exhibit a relative deficiency in reuptake compared to other regions. The second aim tests the hypothesis that failure or saturation of astrocytic reuptake mechanisms underlies CSD ignition. Our preliminary data on CSD propagation shows astrocyte activation well in advance of the wave, and suggests a failure of potassium reuptake at the advancing wavefront. We will genetically ablate key astrocyte mediators of potassium reuptake as the cortex is brought to CSD threshold in vivo, in order to test the role of the astrocyte, and determine which mechanism is most important. The third aim asks how CSD, a massive depolarization, is generated in an ostensibly intact brain. Here our preliminary data on sensory cortex susceptibility is particularly important, as it allows us to constrain potentially open-ended experiments. We will systematically test triggers of aura in awake behaving animals while we record from sensory cortex using two photon microscopy.